1. Field of the Invention
This invention relates generally to a foldable solar array and, in particular embodiments, to a folding low concentration solar array that can be deployed and retracted from a space-based support structure.
2. Description of Related Art
Various folding concentration solar array designs have been developed for connection to the body of a spacecraft. Typically, such foldable arrays are composed of a series of solar panels connected edge-to-edge lengthwise by hinge attachments. U.S. Pat. No. 3,667,508 describes a foldable solar array, wherein reflectors are attached widthwise to the opposite ends of each solar panel. U.S. Pat. No. 4,686,322 describes reflectors which are used in conjunction with solar panels.
Such solar arrays may typically be mounted upon deployment booms or yokes which can be extended or retracted from spacecrafts. When the solar array is stowed, such as during the launch of the spacecraft, the reflectors are folded over their respective solar panels and the solar panels are folded together in an accordion-like fashion against or within the spacecraft. When the solar array is fully deployed, the solar panels are disposed in substantially a common plane and the reflectors are folded away from these panels, into a position which concentrates sunlight upon the solar panels.
Typically, such solar arrays include one or more panels supporting solar cells for generating electrical power for a spacecraft or the like. As such, the solar panels of each array must be adequately protected to ensure their proper and continuous function throughout a space mission. For example, during the launch of a spacecraft, the solar panels may be subjected to extreme stresses and vibrations. After the spacecraft has reached space, and during or following deployment of the solar array, the array may be subjected to further stresses and forces which may damage the solar panels. In addition, when the solar array is in a deployed configuration the extreme heat of the sunlight often causes thermal stresses in the solar panels.
In some previous designs of concentration solar arrays, the loads and stresses which normally occur during a spacecraft launch and the deployment of the array itself have been borne by the solar panels. The solar panels in these designs are the structural support members of the solar array. For example, a paper entitled "Retractable Planar Space Photovoltaic Array" presented at the 21st IEEE Photovoltaic Specialists Conference, May 21-25, 1990 ("the IEEE paper") describes a concentration solar array with solar panels constructed from honeycomb panels. This honeycomb structure presumably allows the solar panels to withstand high stresses and loads which are typically borne by structural support members.
The drawback of such a system is that the solar panels, being the structural support members of the solar array, are subjected to much structural and thermal stress and strain during space flight, deployment and retraction. This is undesirable because the solar cells which are disposed on the solar panels can be relatively fragile and sensitive to these stresses and strains. To function as a primary structural support member of the solar array, each solar panel must have a construction suitable to withstand the above-noted stresses and strains. As a result, such solar panels can be relatively heavy, expensive and difficult to repair or replace. However, despite these drawbacks, the industry has continued to rely on the structural integrity of the solar panels to function as the primary or sole structural support members of the solar array.
The tendency to rely upon the solar panels as the primary structural support member is further illustrated in various references, such as U.S. Pat. Nos. 4,394,529 and 4,686,322. The '529 patent describes a solar panel which is comprised of an array of stiffening beams. The '322 patent discloses a number of substrates for solar panels, all of which are honeycomb panel structures for structural strength. Reinforcement ribs are often added to these honeycomb panels to increase the strength and rigidity of the panels in the stowed and deployed configurations.
Folding concentrator style solar arrays have also presented a problem with regard to the protection of the individual solar panels when the array is in a stowed configuration. When the solar array is stowed--that is, when the reflector panels are folded over the solar panels and the array is folded together in an accordion-like fashion--it is necessary to prevent the reflectors or other panels from impacting the solar cell surfaces. In some cases, such as the retractable solar array disclosed in the above IEEE paper, the reflector is designed to avoid touching the solar panels in the stowed configuration.